If Messrs. Huckabee and Romney compete in the next round of primaries and beyond, as they have pledged to do, that forces McCain to spend precious resources from his underfunded campaign and continue the tense internecine battle within the Republican Party. He would much prefer to focus his energies on the Democrats – particularly as their tight nomination battle promises to continue at least through next month, if not longer.

Since McCain's victory in nine of 21 states Tuesday, some party leaders, such as former GOP chair Haley Barbour, have suggested that the time has come for the weaker candidates to drop out and allow the party to coalesce around a presumptive nominee. The problem is that no one can tell Huckabee or Romney what to do. And there is a strong constituency within the party – centered in the conservative wing – that is holding out hope that the sometimes-mercurial McCain can be stopped.

"Both of them [Huckabee and Romney] have supporters who have very, very strong feelings against John McCain," says Dan Schnur, an aide to McCain in his 2000 presidential race who has not worked for any of the 2008 candidates. "If conservatives decide to come together for one last stand against McCain, they can probably derail him. But with such a strong showing from Huckabee, deciding who to coalesce behind becomes a more difficult consideration."

For anti-McCain conservatives, too, there may be some value in seeing Huckabee and Romney continue. The more delegates they accumulate, the greater their clout at the Republican National Convention in September. That could put pressure on McCain as he advances his agenda in the general election and in the formulation of the Republican platform.

On most issues, McCain adheres to Republican orthodoxy. He is a social conservative, a deficit hawk, and one of the Senate's staunchest supporters of the Iraq war. But at times he goes off the GOP reservation – such as with his support for a path to citizenship for illegal immigrants – and he makes conservatives uncomfortable.

"The base of this party wants loyalty to it," says independent pollster John Zogby. "On the other hand, McCain's strategy is going to have to be to play to his strength – which is in the middle – and take advantage of his ability to do that while the Democrats are divided."

Then, Mr. Zogby adds, McCain will have to finesse his differences with conservatives by promising appointments, including a smart choice for running mate. Two names already being mentioned are Mr. Barbour, now the governor of Mississippi, and Charlie Crist of Florida, another popular governor whose endorsement of McCain on the eve of the state's Jan. 29 primary helped the senator to a narrow victory that established his front-runner status.

Exit poll data from Tuesday showed that McCain continued to do well among moderates and voters who value experience as the top candidate quality. He also won a plurality of self-identified Republicans, a feat he had not pulled off in the previous nominating contests.

In California, which McCain won handily despite polls showing a late surge by Romney, the senator's liberal position on immigration appeared to help him. He won among voters who favor a path to citizenship and those who favor a temporary worker program, which together represented more than 50 percent of GOP voters in California, but lost to Romney among the 38 percent who favor deportation.

McCain also fared well among Latino Republicans in California – 14 percent of the GOP electorate there, winning a 35 percent plurality of them. He was also the top vote-getter among white GOP Californians (40 percent) and Asians (63 percent).

Winning California was important to McCain; a Romney victory there would have given him bragging rights and greater claim to legitimacy for staying in the race. But California was not a winner-take-all state, in terms of delegate allocation. In the all-important delegate count, McCain won most of the winner-take-all states – New York, New Jersey, Arizona, Missouri, Connecticut, Oklahoma, and Delaware.

According to Associated Press estimates, which were not complete, McCain has amassed 613 of the 1,191 delegates needed to secure the GOP nomination. Romney has 269, Huckabee has 190, and Rep. Ron Paul of Texas has 16.

Romney was reported set to have "frank discussions" with his staff on Wednesday about the future of his campaign, even as he promised his supporters Tuesday night that he would fight on to the party convention. Some analysts say Romney wants to preserve the option of running in 2012, if a Democrat wins in November. If he continues to pour his own money into his 2008 campaign beyond the point of any reasonable expectation of victory, he could damage his standing in the party.

But the biggest question after Super Tuesday was how or if McCain and his conservative elite antagonists, such as talk-radio host Rush Limbaugh, can come to some kind of truce over McCain's ascendancy. Tuesday afternoon, evangelical leader James Dobson released a statement announcing that he would sit out the election if McCain is nominated. If large numbers of evangelicals follow suit, that could doom McCain.

In his victory speech to supporters Tuesday night, McCain aimed for party unity.

"I am as confident tonight as I have ever been that we can succeed in November by uniting our party in our determination to keep our country safe, proud, prosperous, and free and by again making a persuasive case to independents, and to those enlightened members of the other party, that the great Ronald Reagan claimed for our party," he said.

Analysts suggest that McCain's best argument to his GOP critics is electability.